The present invention relates to a soft plastic contact lens which is most useful in correcting visual deficiencies in the eye and more particularly to a contact lens of an hydrophilic, soft ophthalmic plastic material commonly known as gel lens material which not only enhances visual resolution in presbyopic ametropia but also is effective in pre-presbyopic ametropia.
During the last twenty-five years hard contact lenses have become effective therapeutic devices for the treatment of ametropia with capabilities far in excess of regular ophthalmic lenses. Although their use as a cosmetic replacement for regular ophthalmic lenses is the primary reason for their increased utilisation, they are, in fact, more effective in the treatment of most cases of high ametropia, anisometropia and irregular astigmatism than conventional spectacles.
In recent years their use has significantly increased and a demand for their wider application is manifest, especially so among presbyopic patients who have been wearing contact lenses for the last twenty or more years. These patients are now at the age where they require supplemental lens power over and above their contact lens correction in order to maintain normal vision function at near distances in the order of 13-16 inches. Many types of bifocal contact lenses have been designed and fitted with extremely limited success and acceptance. The simplest solution has been the use of spectacles for near tasks in conjunction with continuing contact lens wear and, in many cases, this has led to the abandonment of both in favour of regular ophthalmic bifocal lenses, with their inherent limitations. Regular bifocal lenses are rather restrictive on head and eye movements and therefore their value is reduced in many occupations. Development of contact lenses useful for both near and far distances has been long sought after.
Soft, hydrophilic or hydrated gel, ophthalmic plastic materials have been developed within the last ten to fifteen years and these materials are being used for contact lenses but no really satisfactory multifocal contact lens of this soft material has so far been produced.
Spherical aberration in the eye has been reduced in recent years by the use of hard plastic spectacle lenses having a front aspheric surface, such as for example in the Bausch & Lomb, American Optical Company, and Orma (trade mark) aspheric acrylic spectacle bifocal lenses used mainly in aphakia therapy. They improve resolution but are similar to regular bifocal lenses. More recently such a construction has been used in the Panofocal (trade mark) hard contact lens for the correction of ocular astigmatism.
In the Wichterle U.S. Pat. Nos. 2,976,576; 3,361,858; 3,408,429; 3,496,254; 3,497,577 and 3,499,862 methods for cutting and producing hydrophilic soft contact lenses are disclosed. Furthermore, in the Seiderman U.S. Pat. No. 3,503,942 a hydrophilic plastic contact lens is disclosed of a specific composition. Soft contact lenses have been developed which are effective in correcting astigmatism in the prepresbyopic eye. They are of toroidal but not aspheric design. However, in none of these patents is a soft contact lens disclosed, fitted to the wearer, which alleviates presbyopic ametropia.